The invention relates to apparatus for manufacturing power transmission belts, but more particularly, the invention relates to apparatus for curing or vulcanizing of such belts.
It is normal practice to build a belt sleeve by plying together superimposed layers of various materials. The belt sleeve includes a first layer of uncured rubber over which is placed a tensile reinforcement of spirally wound cord. A second uncured rubber layer is superimposed over the cord. The belt sleeve is then cured under heat and pressure.
Various methods and apparatus have been devised which devote special attention to the tension section during curing or vulcanization. One such method is taught by U.S. Pat. No. 2,573,642 as issued to Hurry. Another method and apparatus that gives attention to the tension section, is taught by U.S. Pat. No. 3,398,218 as issued to Richmond. Both Hurry and Richmond teach methods for curing belts which have a tensile reinforcement that is variable in length. Under the Hurry method, the tensile reinforcement is stretched as the rubber layers are pressured into the mold. Under the Richmond method, a radially inward differential pressure is first applied to a belt body which somewhat compresses the tension section. Then an outward radial pressure is applied against the belt body as a blowing agent disposed within a rubber material expands.
It has been found that these and similar methods are satisfactory for manufacturing power transmission belts having customary tensile reinforcement which may be either stretched or shrunk tolerable amounts. Tensile reinforcements falling within this category include cotton, rayon, nylon and polyester. But in recent years, industry has created a demand for power transmission belts or higher power transmission capability. The demand established the need for a stronger or higher modulus tensile reinforcement. However, known tensile reinforcements of higher modulus, such as fiber glass and steel, are relatively inextensible and unshrinkable. Another high modulus reinforcement is an aromatic-polyamide sold under the trademark Nomex by DuPont. The unextensible properties of such reinforcements prevents proper curing pressure to be applied to both rubber layers of the belt sleeve during curing or vulcanizing by known methods. For manufacturing reasons, fiber glass cord is preferred over steel cord. However, fiber glass must be carefully handled because it is severely damaged if compressed. Compression loading of the tensile reinforcement is inherent in some known belt sleeve curing methods such as Richmond.